Embedding or sandwiching the conductor of an inductive element in a magnetic material can significantly increase its inductance at a given size or reduce its size while maintaining a given inductance. Similarly, embedding or sandwiching a conductor in a magnetic material can improve containment of the magnetic field generated by current flowing along the conductor: this may be especially valuable if the conductor is formed as part of a semiconductor device such as an integrated circuit, since it can improve signal isolation from other elements of the device.
A reduction in circuit element size is especially valuable for microscopic circuit elements made using semiconductor-type manufacturing techniques such as mask-controlled deposition and etching of materials on a support layer, since it leads to a reduction in occupied chip area which enables more devices to be produced for a given sequence of manufacturing operations and a given overall support layer (‘wafer’) size.
However, ferromagnetic resonance (FMR) losses have restricted the applicability of such devices to below 1 GHz, even using high resistivity ferromagnetic materials.
A report entitled “Soft ferromagnetic thin films for high frequency applications” by Fergen, I. et al. in the Journal of Magnetism and Magnetic Materials vol. 242-245 p. 146-51 April 2002 describes a study of the properties of sputtered thin films of magnetic material at high frequencies.
A report entitled “Ferromagnetic RF inductors and transformers for standard CMOS/BiCMOS” by Zhuang Y et al. in the International Electron Devices Meeting 2002 Technical Digest, IEEE 8 Dec. 2002 p. 475-478 describes an RF inductor comprising an elongate electrical conductor coupled magnetically with a thin layer of magnetic material extending along at least part of the conductor above and below the conductor, the layer having a thickness of 0.5 μm and a lateral dimension of 100, 200, 400 or 800 μm.
A need exists for a practical high frequency thin film electrical circuit element for high frequency applications that has a small occupied chip area.